Nodular graphite cast iron containing calcium and magnesium



March 14, 1967 KAZUJI KUSAKA NODULAR GRAPHITE CAST IRON CONTAINING CALCIUM AND MAGNESIUM Filed June 18. 1963 F l G. i

(Ferrre,Peorlre Form) F! G. 3 Peorli'e. Cemenrie Form) F G.l 2 (Ferrire'. Peorli're Form) (Sorbie Form [/VVE/VTO? KAZUJI KUSAKA Maf United rates Patent dice 3,39,l97 Patented Mar. 14, 1967 3,309,197 NODULAR GRAPHHTE CAST IRON CONTAINING CALCIUM AND MAGNESHJM Kazuji Kusaka, 16--20 S-chome Honkugenuma, Fujisawa, Japan Filed `lune 18, 1963, Ser. No. 288,806

Claims priority, application Japan, Oct. 16, 1962,

l 37/44,791 Claims. (Cl. 75-130) This invention generally relates to nodular graphite cast iron and improvement of its manufacture, and particularly to nodular graphite cast iron, containing calcium and magnesium and to a simplified method of manufacture thereof.

An object of the invention is to provide an improved practice of making a casting contain magnesium as well as a small percentage of calcium, thereby accomplishing excellent spheroidizing and obtaining improved nodular graphite cast iron with reduced mass effect.

Another object of the invention resides in providing a novel method of manufacturing in a simple manner the nodular graphite cast iron, in which method addition of alloy can be accomplished in only two stages, thereby assuring that casting is carried out in a very safe manner and with extreme ease, eliminating possibilities of explosions or like accidents, reducing flash and finally achieving a great saving in the amount of alloy which is added.

Another object of the invention is to provide commercial nodular graphite cast iron of a good quality, moderately priced, which can be obtained by a unique method employing a new addition-agent, composed of halides of such rare earth metals as misch-metal (mixed metal) and calcium-silicon powder, which are inexpensive and easy to handle, in place of costly rare earth metals as such, and magnesium alloy etc.

Other objects and a fuller understanding of the invention will become clear from the following description and claims, taken in conjunction with the accompanying drawing, in which:

FlG. l and FlG. 2 are representations of photos, showing microstructures (X100) of the nodular graphite cast iron, obtained by the method and materials according to,

this invention;

FIG. 3 represents photographic microstructure (X 100) of the -chilled casting, produced in accordance with the manufacturing technique according to the present invention;

FIG. 4 is a representation of a photograph of a microstructure (X100) of the chilled structure, shown in photo 3, after a heat treatment including annealing at 950 C.

FIG. 5 is a representation of a photograph of a microstructure (X100) of one type of as cast nodular graphite case iron according to the invention; and

FIG. 6 is a representation of a photograph showing microstructure (X300) of the lcast iron of FIG. 5 after quenching and subsequent tempering.

It should be noted that all the samples in the representations of the photographs of microstructures have been etched with 3% solution of alcohol nitrate.

The present invention is characterized by the addition,

in the first stage7 of a substance (addition-agent) containing both calcium and magnesium, to the molten iron for desulphurization, and then in the second stage, the molten iron is cast, after causing a chemical reaction in the molten iron by adding one or more of such special salts as MgFz and in an amount as is found necessary, RF3(LaF3, CeF3 and YF3), as well as a proper additionagent such as Ca-Si or Ca-Si type alloys, which is capable of reducing the metal, contained in the added salt and the casting so obtained can have C and Si contents which are unusually highly variable, approx. from 2.5 to 4.2% and approx. fromvl to 6% respectively, and accordingly, spheroiding can be made possible with gray pig iron or white pig iron.

According to this invention, the method of manufacturing nodular graphite casting is carried out in two separate stages, in both of which a substance (addition-agent) is added to the molten iron, so that easy-to-cast nodular graphite iron is obtained by a very simple practice in a safe manner, as will be explained hereinafter. For a better understanding of the comparative advantages of the manner of manufacturing the nodular graphite cast iron pursuant to this invention with respect to prior art, there will be Adescribed briefly an example of the prior method of manufacturing nodular graphite cast iron by the addition of magnesium alloy.

Method for manufacturing nodular graphite cast iron, so far known most widely, is a method as patented in U.S. Pats. Nos. 2,485,760 and 2,485,761, which relate to a technique of casting, pursuant to which first such alloys as Cu-Mg, Ni-Mg and Fe-Si alloy are added to the said iron, so that the residual content of Mg in the cast iron is @O4-0.50% and the cast iron is characterized by spheroidization of most of the contained graphite and the content of C and Si as defined by the following formula;

This means that cited method of manufacturing nodular graphite cast iron concerns only cast iron with chemical compositions that give a hyper-eutectic structure.

More recently, a method of desulphurization in which CaCZ (calcium carbide) has been used more and more in order to reduce the percentage of sulphur in the molten iron before the addition of Mg alloy thereto in a practical process of producing the nodular graphite cast iron, as this is apparently more convenient. It should, however, be noted that the addition of MgV alloy, in accordance with Canadian technique of making nodular graphite cast iron, has such grave drawbacks as surfacing of the added alloy in the molten metal due to the fact that the specific gravity of the alloy is less than that of iron and the possibility of the occurrence of an explosion, accompanied by severe flash, when the said addition-agent makes contact with the surface of the molten metal when it is changed. These drawbacks make necessary the use ofa preventive phosphorizer, plunger or Ventilating apparatus etc. of a special design. Besides the above, the said Canadian-invented method of nodular graphite cast iron making also requires fairly complicated operating procedures, as all foundry specialists are well aware.

The present invention is advantageous in that it can remove almost all of the engineering disadvantages described above. The new process of manufacturing nodular graphite cast iron is quite free from flashing or explosion danger, due to the novel property of the special addition-agent to be added in two different stages, first and second, and the addition of the addition-agent is conducted by su-ch a very simple method as place-and-tap or charge and an excellent nodular graphite cast iron, which is highly acceptable for successful casting, can be v assured.

l Si a n. Caoz 60%, Canti, 20%, ein .10%, Fest 10%. CaFz CaO 20%, MgFg 30%, Ca-Si 30%.

It has been found experimentally that any of these compounds-assures improved desulphurization without any danger of explosion when a small quantity (l2% is placed at the bottom of the ladle before tapping ltherein v of the molten iron7 or charged as a package into the molten iron being tapped into the ladle, and facilitates a simple operation in the subsequent second stage.

Conrmation with `respect to the above-described advantage, of this invention is seen in Table 2 which shows Well as a safe and simple operation of producing nodular graphite cast iron.

(2) Novel technique of obtaining sphcroidized graphite (2nd stage).

This position of the invention concerns micro-addition of one of the compounds (addition-agent), Bl-B5 as listed in Table 3, in the second stage, to the molten iron, which has preliminarily been desulphurized by means of the addition of one of the compounds, Al-A5, in the first stage.

Addition of the compound in the second stage can be either by Injection place-and-tap or charge practice, with a very high safety and without danger of ilashing so that a very simple method of spheroidizing results. Such an advantage, together with the unusual sinipicity of operation require-d for the addition, represents an apparently substantial advance for the new method of spheroidizing pursuant to this invention in relation to known method of spheroidizing.

TABLE 3 Final residue, percent N o. oi Description of compound Percent of Method of compound (2nd stage) addition addition Mg Ca R MgFg, Ca-Si. 2 Flamand-tap... 0. 052 Trace MgFz, RFQ, Ca 1.5 do i 0.028 Trace A small quantity.

MgFz, Ca-Si-Mn- Trace MgF2, Ca-Si-R Trace Do. CeF3.YF3.LaF3, Ca-Si, Fe-Si.. Trace DoA Noris 1.Letter R in the Type of compound (2nd staged'y column means rare metal,` including Cc, La

Y and the like.

NOTE 2.Chemical composition of used alloys: Ca-Si-Ca, 32%; Si, 60%; Residual Fe. CaSi-`\in-Ca,

16%; Mn, 18%; Si, 58%A a comparison of results of the desulphurization, by addition of the compounds of Table l 4pursuant to this invention and those with convention-al known CaCz powder by powdering hot molten iron (0.083% from the cupola.

Ca-Si-R-Ca., 18%; R, 18%,' Si, 52%.

The result of a chemical analysis of alloys in the compounds in each row in Table 3 for compounds Bl-B5 shows the result of the addition of one of the compounds from B1 to B5 to the molten iron with chemical cornon A5 (Composition of the invention).

It is apparent from Table 2 that both the addition of known addition-agent CaCz for desulphurization and addition of the compounds (addition-agent) Ail-A5 to the molten iron require only a simple operation for addition, resulting in, however, substantial difference in the desulphurizing effect, in absolute favor of the new compounds used pursuant to the present invention.

The reason for the above mentioned ditference is presently unknown, but may be considered to be favorable multiplication of inherent desulphuriza-tion effects of both Ca and Mg of the new compounds which perhaps are decomposed in hot molten iron, resulting in such effective action of activated Ca an-d Mg that they are combined with the sulphur content of the mol-ten iron into CaS yand MgS which in turn is removed from the molten iron in the form of a scum. Mg may, after completion of sulphurization, be micro-'residue or totally purged.

All of the compounds (addition-agent), according to this invention, are novel agents which .have been reported in none of the prior publicized literature, and assure, when applied in the first stage for desulphurization, satisfactory spneroidizing in a subsequent second stage, as

position of C 3.55%, Si 2.12%, Mn 0.42%, P 0.08%, remainder Fe, which has been desulphurized in the first stage, after which the said molten iron has been found characterized by nodular graphite structure, achieved by a very simple operation. `lt has also been confirmed that the Ca-Si in any of the Bl-BS compounds, can be partially replaced by a micro-quantity of CaC2, CaN2 and Fe-Si and Mg-Si alloys. it is important to note that the molten iron after treatment in the second stage still contains a micro-quantity of Ca and a small-quantity of Mg, both of which give a valuable advantage in the preisent invention.

After treatment in the second stage, the molten iron may or may not contain a residue of R. This results from chemical reaction of MgFZ, lR133 (CeF3, La'F3, YF3) etc. in the molten iron in the second stage. Such reaction seems to have been caused by the reduction to Mg or R in accordance with, for example, the following reaction formula or a similar-one.

It also seems that addition of CaSiZ, in an amount which is a little more than the mol ratio required for reaction with MgF2 or RF3 has caused the mixture of molten Ca, resulting in micro-residues of Mg, Ca and R (Ce, La, Y) etc. in the molten iron, which seems substantially to have been favorable for spheroidizing of the graphite.

The technique of adding a compound, comprising MgFz or one or more of RF3 alloys (CeF, LaF3, Y'FB) and Ca-Si or Ca-Si type alloy, to the molten iron in the second stage of treatment pursuant to this invention is very easy from a practical standpoint and insures proper alloy-control in the molten iron of new metals reduced from the tluorides of the member alloys, and calcium from Ca-Si alloy, and there is no danger of explosion and severe dashing. Cast iron so manufactured always contains a micro-quantity of residual Mg and Ca, which can be detected by emission spectroscopic analyzing practice (0.001 0.03% Ca), and sometimes may have a residue of R.

(3) Practice of casting and time from inoculating to casting in accordance with present invention.

The technique of manufacturing nodular graphite cast iron purs-uant to this invention is characterized by special treatments to be conducted in two different stages, the first and the second, as described above, but it is possible that a micro-quantity of Fe-Si or other similar alloy will have to be added after treatment in the second stage.

Molten iron, treated for casting pursuant to the present invention, is generally characterized by beautiful film play and improved fluidity, which does not necessarily require inoculation.

Another advantage of this invention, which is Worth notice, is that the molten iron, treated in the second stage, pursuant to the present invention, can remain effective for successful spheroidizing of graphite for -as long as 20 minutes before pouring for casting.

Prior practice, in accordance with which Mg alloy is added to the molten iron, has been, as all foundry specialists are well aware, subjected to the definite disadvantage that the molten iron, to which Fe-Si has been inoculated after spheroidizing treatment, becomes less sensitive to the spheroidizing of graphite, if it has not been completely poured for casting within 20 minutes after previous treatment.

Meanwhile, the molten iron which has been so treated that there remains therein residual Mg and Ca, or Mg and Ca plus R in accordance with this invention, is characterized in that successful spheroidizing of the graphite can be achieved even when it is poured as long as 20 minutes or so after previous treatment in the second stage. This represents one of the valuable advantages of the spheroidizing technique pursuant to this invention, and is substantially useful for practical foundry operation.

(4) Unusual uniformity of metallurgical structure of the nodular graphite cast iron, manufactured pursuant to present invention.

Nodular graphite cast iron, obtained by the process of this invention (1st stage and 2d stage) and containing Mg and Ca, has another valuable advantage in that it has an unusually uniform metallurgical structure.

This fact is backed up by, for example, the results of various testings to check the segregation, distribution of sulphur content and short hardness, applied to longitudinal sections of the test castings, obtained from molten iron with a chemical composition of C 3.5%, Si 2.1%, Mn 0.65%, P 0.064%, S 0.008%, Mg 0.042%, Ca 0.010%, and remainder Fe, realized by applying a technique of spheroidizing in accordance with this invention (lst stage-Hd stage), and poured into 3 different circular sand molds with 50, 100 and 150' mm. p, all of which showed highly uniform structure in every detail.

Distribution of hardness, in, for example the 150 mm. o test casting, is'represented by Table 4, from which it is quite apparent that the present invention assures much better hardness distribution than the prior method of manufacturing regular conventional ductile cast iron.

Result of chemical analysis of compared specimen (R.D.C.I.).C, 3.5%; Si, 1.8%; Mn, 0.60%; P, 0.06l%; S, 0.010%; Mg, 0.070%; Ca, 0%, remainder Fe.

`From the above, it can be reasonably concluded that the manner and process of manufacturing nodular graphite cast iron pursuant to this invention, assures the production of excellent nodular graphite cast iron in a very safe and simple foundry operation, even though pouring is made a longer time after previous treatment for spheroidizing, which according to this invention, is to be carried out in two different stages, employing special compounds (addition-agent), and in the cast iron obtained are residues comprising a small quantity of Mg (0.01- 0.i%) and a micro-quantity of C (0.001-0.03%) which, however, can be detected by testing technique.

Besides the above, nodular graphite cast iron, manufactured in accordance with this invention may or may or may not contain one or more of such elements as R (La, Ce, Y) and the like, and moreover with respect to the C and Si content, the spheroidizing according to the present invention, is not necessarily limited to the preceding quantitative relation between C and Si. The chemical composition of the cast iron to which the present invention is applicable for spheroidizing includes grey pig cast iron and white pig case, covering a wide range of carbon content (about 2.5-4.2% and Si content about l-6%), as well as to alloys of cast iron, which may contain also Ni, Cr, Mo and Cu, etc.

The steps in performing this invention are described hereunder- In the first stage, a compound containing Ca and Mg is added to the molten iron for desulphurization, and then in the second stage, MgFg, if necessary, and one or more of RF3 (CeF3, LaF3, YFQ), as well as one or more of Ca-Si, Ca-Si-Mn and Ca-Si-R alloys, required for satisfactory reduction of the Mg and R compounds are jointly added for successful spheroidizing of the graphite.

It should be noted that, in the second stage, MgF2 may be replaced by Mg-Si alloy or Ca-Si alloy, and the Ca-Si type alloy may be partially replaced by CaC2, CaN2 or Fe-Si alloy and Mg-Si type aloy iron.

Moreover, after treatment in the second stage, inoculation with Fe-Si alloy or Ca-Si type alloys can be carried out if necessary.

It is to be understood that for the performance of this invention, desulphurization in the first stage can be omitted and only treatment in the second stage will be carried out, when the cast iron for spheroidizing pursuant to this invention is characterized by very favorable original chemical composition, namely, when such iron has a sulphur content nearly as low as that achieved by desulphurization resulting from the treatment in the rst stage in accordance with this invention.

It is also to be understood that the molten iron, desulphurized in the tirst stage according to this invention, is in metallurgical condition most suited for another treatment for spheroidizing in a subsequent stage, and accordingly, addition of conventional Mg alloy provides a slight hope for substantial effect of spheroidizing.

The following examples serve to illustrate themanu- 'facture of nodular graphite cast iron in pursuant to this invention. Y

if Example I Hot molten iron, with a chemical composition of C 3.6%, Si 2.8%, Mn 0.35%, P 0.07%, S 0.076%, and remainder Fe, was poured out of the acid cupola into the first ladle, was treated for desulphurization by 2% addition of one of the compounds, A (CaCZ 80%, MgF2 land Ca-Si 10%) Table 1, by place-and-tap practice and then was slagged off.v Subsequently, one of the graphite spheroidizing compounds B (MgF2 35%, LaF3 5%, Ca-Si 60%) Table 3 was added in an amount of 1.5% to the molten iron, being re-poured into the second ladle. A specimen cut from the cast iron obtained from the said treated molten iron showed a good microstructure as illustrated in FIG. 1 wherein ferrite, containing w-all spheroidized graphite, is prevalent. The result of an analysis of the specimen has shown the chemical compositions to be C 3.5%, Si 3.4%, Mn 2.34%, P 0.068%, S 0.012%, Mg 0.034% and trace of Ca, remainder Fe.

Example II The structure of the cast iron so obtained suggested a good spheroidized graphite casting as shown in FIG. 2, and chemical analysis revealed the chemical composition to be C 3.62%, Si 3.1%, Mn 0.42%, P 0.072%, S 0.011%, Mg 0.028%, Ca 0.015%, and remainder Fe.

Example III Mixed 60% ductile iron, 40% steel scrap, 19% Fe-Mn and coke and lime were charged into an electric arc furna-ce for melting down, and then treated for desulphurization by adding about 2% of one of the desulphurization compounds A pursuant to this invention (CaC2 70%, dolonite powder and finally the molten iron, so obtained, was tapped into the ladle.

In carrying out tapping of the molten iron into the ladle, 2% of the mixture of 40% MgF2 and 60% Ca-Si as a compound B was added as the second stage treatment, followed by adequate stirring.

The metallurgical structure of the cast iron so obtained was that of white pig iron containing spheroidized graphite as illustrated in FIG. 3, and the result of an analysis thereof showed the chemical composition to be C 3.38%, Si 2.1%, Mn 0.65%, P 0.052%, S 0.007%, Mg 0.075%, Ca 0.010% and remainder Fe.

This hard cast iron, after heat treatment, had the structure of a soft iron as shown in FIG. 4 characterized by the presence of spheroidized graphite in ferric matrix, said heat treatment comprising first holding the iron at 950 C. for 2 hours and then at 720 C. for 2 hours and finally furnace-cooling it.

Example l V To hot molten iron, obtained in an electric arc furnace, in the similar manner as in Example lll, was added 2% of compound A3, consisting of CaC2 90%, MgFg 5% and CaSi 5% by place-and-tap practice for desulphuriz'ation when the said molten iron was being tapped into the ladle, and then there was added 1.5 of another compound B, composed of MgF2 30%, Ca-SiR alloy 10% and Ca-Si alloy 60%, and in addition 0.3% of Fe-Cr was added to the molten iron which, then was stirred and finally poured into the sand mould. Cast iron so obtained was found characterized by the presence of bulls eye spheroidized graphite in the pearlite matrix as illustrated in FIG. 5. A chemical analysis of such cast iron revealed the chemical composition to be C 3.35%, Si 2.42%, Mn 0.60%, Cr 0.15%, P 0.037%, S 0.008%, Mg 0.042% and Ca trace, and the remainder Fe.

The above mentioned cast iron was then heated up to 910 C. hardened in oil, and finally tempered at 400 C., as a result of which was produced a sorbite structure wherein spheroidized graphite is noted as shown in FIG. 6.

It has been successfully confirmed that the specimen of Example IV contains a small quantity of Cr, but the additional inclusion of one or more of Ni, Mo and Cu will not adversely affect formation of spheroidial graphite, if it is not substantial. According to the spirit of this invention, when desulphurization in the first stage, and spheroidizing of graphite in the second stage are to be done in one common ladle, it is unobjectionable first to take 2/ 3 of the molten iron in the ladle for desulphurization and then to tap the remaining 1/3 into the same for spheroidizing.

In the above, this invention has been described, stressing some specific embodiments, but it should be understood that many widely different embodiments of this invention may, with respect to individual details and/o1' combinations and/or other particulars, be carried out without departing from the spirit and scope of this invention, and it is to be understood that the present invention is not limited to the specific embodiments thereof except as defined in the appended claims.

What I claim is:

1.. A method of making nodular graphite cast iron, comprising adding to molten iron suiiicient of a mixture of at least one magnesium containing desulphurizing compound and at least one calcium containing desulphurizing compound for desulphurizing the molten iron to a sulphur content less than .015%, then adding to the desulphurized molten iron a spheroidizing agent comprised of a mixture of at least a magnesium halide compound and a reducing agent for said magnesium halide compound, said reducing agent including at least a major portion of Ca-Si, whereby there is produced an excellent nodular graphite cast iron, danger of fiashing during adding of the spheroidizing agent is 'substantially eliminated, and the elfective spheroidizing time is more than 20 minutes.

2. A method as claimed in claim 1 in which the desulphurizing compounds are present in a total amount of from 1-2% by weight of the molten iron, and the spheroidizing agent and reducing agent are present in a total amount of from 1.5-2% by weight of the molten iron.

3. A method as claimed in claim 1 in which the mixture of desulphurizing compounds is taken from the group of mixtures consisting of CaC2 80%, MgF2 10%, Ca-Si 10%; CaC2 70%, dolomite 20%, Na2CO3 10%; CaCZ MgF2 5%, Mg-Si 5%; CaC2 60%, CaNz 20%, MgF2 10%, FeSi 10%; CaFz 20%, CaO 20%, MgFZ 30%, Ca-Si 30%.

4. A method as claimed in claim 1l in which the spheroidizing agent is MgFZ and the reducing agent is a reducing agent taken from the group consisting of Ca-Si having the composition Ca 32%, Si 60% and remainder Fe, Ca-Si-Mn having the composition Ca 16%, Mn 18%, Si 58%, and Ca-Si-R having the composition Ca 18%, Si 52% and R 18%, wherein R is a rare earth metal taken from the group consisting of Ce, La and Y.

5. A method as claimed in claim 1 in which the spheroidizing agent is a mixture of MgF2` and RFS, where R is a rare earth metal taken from the group consisting of Ce, La and Y, and the reducing agent is Ca-Si having the composition Ca 32%, Si 60%, and remainder Fe.

6. A method of making nodular graphite cast iron, comprising adding to molten iron suficient of a mixture of at least one magnesium containing desulphurizing compound and at least one calcium containing desulphurizing compound for desulphurizing the molten iron to a sulphur content less than .015%, then adding to the desulphurized molten iron a spheroidizing agent comprised of a mixture of rare earth fiuorides and a reducing agent for said fluorides, said reducing agent including at least a major portion of Ca-Si, whereby there is produced an excellent nodular graphite cast iron, danger of flashing during adding of the spheroidizing agent is substantially eliminated, and the effective spheroidizing time is more than 20 minutes.

7. A method as claimed in claim 6 in which the desulphurizing compounds are present in a total amount of from 1-2% by weight of the molten iron, and the spheroidizing agent and reducing agent are present in a total amount of from 1.5-2% by Weight of the molten iron.

8. A method as claimed in claim 6 in which the mixture of desulphurizing compounds is taken from the group of mixtures consisting of CaCg 80%, MgF2 10%, Ca-Si 10%; C21C2 70%, dolomite 20%, Na2CO3 10%; CaC2 90%, MgF2 5%, Mg-Si 5%; CaC2 60%, CaN2 20%, MgFz 10%, FeSi 10%; Cal-72 20%, CaO 20%, MgF2 30%, Ca-Si 30%.

9. A method as claimed in claim 6 in which the sphe- 10. A method as claimed in claim 1 in which said reducing agent contains a minor portion of a compound taken from the group consisting of CaC2, CaNz, Fe-Si and Mg-Si.

References Cited by the Examiner UNITED STATES PATENTS 2,552,204 5/1951 Morrogh '75--130 2,662,820 12/1953 Crome 75-130 2,750,284 6/1956 Ihrig 75-130 2,814,559 11/1957 Clark 75-130 X 2,821,473 1/1958 Moore 75-130 2,867,555 6/1959 Curry 75-130 X 2,922,713 1/1960 Moore 75-130 2,948,605 8/1960 Ihrig 75-130 2,980,530 4/1961 Crome 75-130 DAVID L. RECK, Primary Examiner.

roidizing agent is a mixture of CeF3, YF3 and LaF3, and 20 P. WEINSTEIN, Assistant Examiner.

the reducing agent is a mixture of Ca-Si and Fe-Si. 

1. A METHOD OF MAKING NODULAR GRAPHITE CAST IRON, COMPRISING ADDING TO MOLTEN IRON SUFFICIENT OF A MIXTURE OF AT LEAST ONE MAGNESIUM CONTAINING DESULPHURIZING COMPOUND AND AT LEAST ONE CALCIUM CONTAINIG DESULPHURIZING COMPOUND FOR DESULPHURIZING THE MOLTEN IRON TO A SULFPHUR CONTENT LESS THAN .015%, THEN ADDING TO THE DESULPHURIZED MOLTEN IRON A SPHEROIDIZING AGENT COMPRISING OF A MIXTURE OF AT LEAST A MAGNESIUM HALIDE COMPOUND AND A REDUCING AGENT FOR SAID MAGNESIUM HALIDE COMPOUND, SAID REDUCING AGENT INCLUDING AT LEAST A MAJOR PORTION OF CA-SI, WHEREBY THERE IS PRODUCED AN EXCELLENT NODULAR GRAPHITE CAST IRON, DANGER OF FLASHING DURING ADDING OF THE SPHEROIDIZING AGENT IS SUBSTANTIALLY ELIMANATED, AND THE EFFECTIVE SPHEROIDIZING TIME IS MORE THAN 20 MINUTES. 